The straight-chain conjugated diene is a useful compound, for example as a starting material for producing synthetic rubber or an intermediate of very large number of compounds. For example, butadiene is a main raw material of styrene-butadiene rubber, nitrile-butadiene rubber, and ABS resin. In addition, butadiene has been used for synthesis of adiponitrile that is a precursor of nylon synthesis as well as synthesis of chloroprene that is a precursor of chloroprene rubber, sulfolane that is used as a solvent and 1,4-butanediol that is important as a synthetic intermediate.
A straight-chain conjugated diene is generally produced through naphtha cracking or olefin dehydrogenation. Through these manufacturing methods, the straight-chain conjugated diene is produced as one component of the reaction mixture. Conventionally, separation and condensation of some ingredients from a mixture of gases or liquids containing organics has been carried out by distillation, azeotropic distillation, solvent extraction/distillation, or with an adsorbent, depending on the properties of the intended substances. However, these methods have drawbacks that a large amount of energy is required or the applicable scope of objects intended to be separated and condensed is restrictive.
An alternative to these methods has been proposed, which is membrane separation and condensation using a polymer membrane or an inorganic membrane, but the polymer membrane has a problem that it is deteriorated in performance due to heat, chemical substances or pressure.
Consequently, various inorganic membranes have been proposed, which are excellent in chemical resistance, oxidation resistance, heat resistant stability, and pressure resistance. Among them, a zeolite membrane has been expected to exhibit high separation performances.
Crystalline alumino-silicate generally termed as zeolite, has fine spaces of molecular sizes (nano-space) in one crystal and is referred to as “molecular sieve”. There exist many types such as LTA (A-type), MFI (ZSM-5-type), MOR, FER, FAU (X-type, Y-type) and the like classified by their crystalline structures. Zeolites with such peculiar higher-order structures, perform a shape-selective function (molecular sieve function), an adsorption separation refining function, an ion exchange function, a solid acid function, and a catalyst function and thus are used in a wide variety of industrial fields.
In the case of using a zeolite membrane for separation and condensation, a zeolite membrane composite having a zeolite formed into a membrane on a support is usually used. A separation method using a zeolite membrane composite is known to be able to separate straight-chain butane (n-butane) and side-chain butane (isobutane) that are hydrocarbon isomers having 4 carbon atoms (see Patent Literature 1).